git merge <tag> behavior

Hi,

While trying to reproduce/understand the problems[1][2] I was facing when using Google's Git repo tool[3], I've found minor problems in Git:

1) there's no mention of the git merge <tag> behavior in git-merge.1

When asking Git to merge a tag (such as a signed tag or annotated tag), it will always create a merge commit even if fast-forward was possible. It's like having --no-ff present on the command line.

It's a difference from the default behavior described in git-merge.1[4]. It should be documented as an exception of "FAST-FORWARD MERGE" section and "--ff" option description.

2) git merge <tag> VS git merge <object-id>

If <tag> is an object (not a lightweight/reference tag), git merge <tag> will by default create a merge commit with the tag message. Additionally, the signature check will be reported as comment, for example:

    Merge tag 'v1.12.2' into branch-v1.12.2

    repo 1.12.2

    # gpg: Signature made Fri Mar  1 18:36:42 2013 CET using DSA key ID 920F5C65
    # gpg: Good signature from "Repo Maintainer <repo@android.kernel.org>"
    # gpg: WARNING: This key is not certified with a trusted signature!
    # gpg:          There is no indication that the signature belongs to the owner.
    # Primary key fingerprint: 8BB9 AD79 3E8E 6153 AF0F  9A44 1653 0D5E 920F 5C65

But, if you use the tag object-id instead of its name, for example using git merge `git show-ref <tag>`, the tag is not recognized and the signature is not checked. Git still create a merge commit, but doesn't prepare a commit message with the tag message and the signature:

    Merge commit 'ac22c7ae2e652f63366b65ee23122292d3564fff' into
branch-ac22c7ae2e652f63366b65ee23122292d3564fff

It would be great to have Git using the tag message and check the signature.

3) Merge options can't be overridden.

If I modify .git/config to set a merge option, for example forcing fast-forward merge, this option cannot be overridden on command line:

Example 1:

    $ cat .git/config:
    [branch "master"]
            mergeoptions = --ff-only

    $ git merge --no-ff <tag>
    fatal: You cannot combine --no-ff with --ff-only

Example 2:

    $ cat .git/config:
    [merge]
           ff = only

    $ git merge --no-ff <tag>
    fatal: You cannot combine --no-ff with --ff-only

Setting the merge options in config should overridden by command line.

Regards.

[1] issue 135: repo: repo sync should force fast-forward merge https://code.google.com/p/git-repo/issues/detail?id=135

[2] Issue 136: repo: repo sync should use the tag name instead of object identifier of the tag https://code.google.com/p/git-repo/issues/detail?id=136

[3] git-repo - repo - The multiple repository tool http://code.google.com/p/git-repo/

[4] git-merge(1) Manual Page https://www.kernel.org/pub/software/scm/git/docs/git-merge.html